1. Field of the Invention
The present invention relates to a machine for sealing cardboard boxes of constant height.
2. Description of the Related Art
Known machines for sealing cardboard boxes comprise a general a bed describing a table for support and advancement of the boxes, devices for pulling the boxes along said supporting table, and at least one taping unit supported in a raised position above said supporting table in such a manner as to engage with the top of the box and apply thereto a sealing adhesive tape during advancement of the boxes along said supporting table.
Said machines are divided in two classes: those for boxes of constant shape (even though it may vary from one series of boxes to the next) and thoses for boxes of continuously changing shape.
Machines of the first class are distinguished from those of the second class by having operational members, in particular the upper taping head, in a fixed position during a work cycle on a series of boxes but preliminarily adjustable at the beginning of a subsequent cycle to adapt the machine to a possibly different series of a subsequent series of boxes.
To permit the aforesaid fixed adjustable arrangement of the upper taping head, presently known machines have the upper taping head mounted on a vertically movable cross-piece engaged at the ends with two supporting guide columns fixed to the bed at the two sides of the box support and advancement table. A threaded rod housed in and engaged in a rotating manner with one of the two columns and fitted with a control crank is engaged with a nut screw fixed to the movable cross-piece to raise and lower said cross-piece and hence the taping head to the position required each time for the height of the boxes to be sealed. For large heavy machines a second screw engagement may be provided in the other column, which otherwise acts only as a guide, using a second threaded rod connected operationally to the first by a chain which develops from one column to the other inside a protective hood under the box support table. See U.S. Pat. No. 4,161,138.
Screw adjustment systems of this type are widely used and ensure correct adjustment of the taping head position. In the version described above they have however the drawback of requiring high columns to ensure control and guidance of the movement of the cross-piece to heights such as to allow passage and sealing of very high boxes. As a result the fixed columns must have the maximum height expected for the highest boxes with the consequent high fixed overall dimensions, which are useless for low boxes. The threaded rods must be very long to the detriment of their strength. At the same time in the version with two threaded rods connected by a chain, the presence of the chain prevents moving the columns upward from the bed to allow access for very high boxes.